An article published on AutomotiveWorld.com in July, under the heading ‘Whole life emissions compliance – a complex challenge‘, highlighted the unavoidable difference between statutory emission limits, especially for the NOx and particulates in diesel exhaust, and the levels which are feasibly measurable once a vehicle has gone into service.
The relatively poor accuracy of on-board diagnostic (OBD) sensors and the equipment used for emissions measurement during routine roadworthiness inspections necessitates an exceedance allowance. That in turn, wittingly or otherwise, makes provision for deterioration in the condition of the engine and its accompanying aftertreatment system. Thanks to improvements in diesel technology, evident most obviously in advances in materials for key components, ‘wear and tear’ is a term far less commonly used than it once was.
Seven or even eight injection events in combination with maximum nozzle pressures of up to 2500bar are now being achieved.
Nevertheless, the performance of vital parts of the powertrain must inevitably decline over the expected lifetime of a modern truck or bus engine, where a million kilometres of operation before major overhaul is no longer unusual. Nowhere is such deterioration in performance more critical than in a diesel fuel system, where increases in injection pressure and in the number of injection ‘events’ per cycle have risen inexorably in the last decade or more. Seven or even eight injection events in combination with maximum nozzle pressures of up to 2500bar are now being achieved.
Denso, the Japanese fuel system supplier, says it will achieve common-rail system nozzle pressures as high as 3000bar in the foreseeable future. That implies an ability to start injection later in the cycle, ie closer to top-dead-centre, together with earlier cut-off, thereby achieving more complete combustion of the fuel, to the benefit of consumption and particulate emissions. Alternatively – or additionally – advantage can also be taken of higher injection pressures to obtain greater atomisation of the fuel, typically through a greater number of spray holes but with a reduced cumulative hole size.
In order to make full use of such ultra high pressures, says Denso project engineer Xiumei Wang, “an increase in injection accuracy performance is essential, in particular multiple injection accuracy”. To that end Denso has developed an injector incorporating a pressure sensor as the basis for what the company calls its i-ART (intelligent accuracy refinement technology) system.
Denso, the Japanese fuel system supplier, says it will achieve common-rail system nozzle pressures as high as 3000bar in the foreseeable future.
Through closed-loop control, the i-ART system is claimed by Denso to ensure that optimum multiple-injection quantity and timing are maintained throughout a vehicle’s lifetime, by automatically compensating for inevitable deterioration, not only within the fuel system but elsewhere in the powertrain. The company points out that the system promises to reduce in-service workshop man-hours currently devoted to fuel system calibration checks. The technology also holds out the prospect of ensuring more confident OBD emission law compliance, implying fewer fault-code alerts.
Heavy-duty diesels look set to benefit first from Denso’s i-ART technology. The light-duty sector is arguably in less need of such a refinement. Car and van diesel powertrain durability is less of an issue, because of what is a generally shorter operational lifetime, at least in kilometre terms.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Alan Bunting has a background in engineering, and has been writing on commercial vehicle and powertrain related topics since the 1960s. He has been an Automotive World contributor since 1996.
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